Intrauterine devices (IUDs) are a commonly used form of contraception. There are two basic types of currently available IUDs—copper-releasing and progesterone-releasing. The copper IUD is a T-shaped device made of polyethylene wrapped with copper wire. The device acts as a foreign body within the uterus and releases copper to produce a chemical effect on the endometrium of the uterus and to alter the production of cervical mucus, thus producing a spermicidal environment.
Progesterone-releasing IUDs are also T-shaped devices and include a cylindrical reservoir containing levonorgestrel, which is released into the uterus over time. The levonorgestrel adds to the foreign body effects to create added spermicidal action and also thickens cervical mucus to act as a barrier to sperm penetration into the uterus.
Although both copper and progestin-releasing IUDs work well for contraception, both have common side effects. The most common side effects with copper IUDs are abnormal bleeding and pain. The most common side effects with levonorgestrel IUDs are hormone-related effects, such as headaches, nausea, breast tenderness, depression and cyst formation. When either copper or hormone/levonorgestrel is used as an active ingredient, it is typically thought that the larger the surface area of copper or hormone exposed in the uterus, the better the contraceptive action of the IUD. Although a larger surface area of exposed copper or hormone creates a higher risk of abnormal bleeding or other side effects, it is thought to be necessary to achieve effective birth control. Thus, for example, currently available copper IUDs typically have an exposed copper surface area of 380 mm squared. Past scientific studies of similarly configured IUDs, but with a reduced copper surface area of 200 mm squared, showed higher failure rates (undesirable pregnancies) in the range of 3%-10%.
In addition to the above shortcomings, many currently available IUDs are at least slightly uncomfortable and/or challenging to deliver into the uterus. All IUDs are delivered through the cervix using a delivery sheath. Although this delivery method works well in many cases, the required size of the currently available IUDs typically requires a sheath having an outer diameter that can cause pain or discomfort upon insertion into a cervix. In some cases, the pain can even be significant. Thus, the size of currently available IUDs and their delivery sheaths is another shortcoming.
Therefore, although existing IUDs work relatively well for their purpose of contraception, there is still a need for improved IUDs. Ideally, such improved IUDs would provide reliable, long-acting contraception with relatively few, minor side effects. At least some of these objectives are met by the embodiments described in this application.